By using the micro-fabrication technology which has realized the improvement in performance and increase in integration density of the semiconductor integrated circuit, the micro electro-mechanical system (hereinafter, referred to as MEMS) technology for forming a mechanical sensor such as a pressure sensor and a acceleration sensor, a miniatured switch, miniature mechanical parts such as a resonator or an oscillator, and a mechanical system has been developed. The MEMS is broadly classified into a bulk MEMS which is formed by processing a silicon substrate itself and a surface MEMS which is formed by repeatedly depositing and patterning thin films on a surface of a silicon substrate. The manufacturing process of the surface MEMS is close to the manufacturing process of semiconductor integrated circuits. The MEMS technologies described above are discussed in pp. 1158 to 1165 of volume 73 (issue 9) of “Applied Physics” (Japan Society of Applied Physics (JSAP), September, 2004).
The U.S. Pat. No. 6,635,506 discloses the technology for precisely forming a shape of a cavity by using a sacrificial layer when forming the cavity used for the MEMS.
The U.S. Pat. No. 6,667,245 discloses an example in which a switch is formed as the MEMS. Also, it mentions that it is possible to form the switch at low cost by using the standard technology for forming a multilayer interconnect of an integrated circuit to form the switch.
The US Patent Application Publication No. 2004/0145056 describes that the MEMS is formed by using a metal layer and a sacrificial layer formed by the standard manufacturing technology of CMOSFET (Complementary Metal Oxide Semiconductor Field Effect Transistor, referred to as CMOS, hereinafter).
The U.S. Pat. No. 5,596,219 discloses the technology for monolithically forming an integrated circuit and a sensor (actuator). This sensor is formed on a sensor layer made of polysilicon by using the surface micro-machine technology.